High strength fasteners
High strength fasteners
(OP)
Does anyone have any experience in using high strength (and then usually low ductility)12.9 quality fasteners for fatigue applications? When I worked in the aerospace industry some years back, 12.9 fasteners were not allowed unless you had very good reasons to use them. Some of my collegaues now say they would not worry about using 12.9 fasteners for fatigue applications. But I don't know. Any one having relevant experience?





RE: High strength fasteners
Design your joint so that the fastener is not subjected to stress ranges where fatigue is a concern.
RE: High strength fasteners
Which industry are you working for?
RE: High strength fasteners
Brian
www.espcomposites.com
RE: High strength fasteners
fasteners. They have their purpose, but not in high fatique situations.
RE: High strength fasteners
The point that MintJulep is making is that threaded fasteners with sufficient preload can be used in cyclically loaded applications without initiation of cracks and subsequent fatigue crack propagation. Fatigue is a specific phenomenon that is not synonymous with cyclic loading, variable amplitude loading, etc.-- it is a condition that results from excessive stresses (or strains) during cyclic loading, variable amplitude loading, etc.
izax1,
Here are some links to previous Eng-Tips threads and other references on fatigue failure of threaded fasteners:
http://www.eng-tips.com/viewthread.cfm?qid=178349
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RE: High strength fasteners
RE: High strength fasteners
Thanks for your patience.
RE: High strength fasteners
To answer Israelkk's question, I work in an industry where too many things fall off due to poor joint design. Or more accurately, a total lack of any joint design.
RE: High strength fasteners
Most of the fasteners I have seen approved for aircraft are, at best, medium strength. The big issue with aircraft fasteners is that they are inspected and tracked, and you have a reasonable expectation that they will work to specification.
I have ordered grade_12.9 fasteners, and the suppliers have shipped grade_8.8. Will the people in your shop see if anything is wrong?
RE: High strength fasteners
Some additional factors to improve fatigue life for these parts include left hand threads, thread adhesive, and yield point tightening.
Do you have any specific questions?
RE: High strength fasteners
RE: High strength fasteners
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RE: High strength fasteners
Left hand threads can help reduce loosening for rotating parts. Loosening leads to preload loss, which is the large cause of fatigue damage. It is a small effect, but an example of details beyond material tensile strength that can affect lifetime.
RE: High strength fasteners
RE: High strength fasteners
RE: High strength fasteners
RE: High strength fasteners
Can you site a study or paper verifying the left hand thread theory? Why aren't all thread left hand if this is true? It is an interesting theory.
RE: High strength fasteners
Here are two items on this subject:
Page 10 of:
http:/
http://www.boltscience.com/pages/failure4.htm
The left hand thread benefit is only valid for rotating parts in the clockwise direction. It doesn't help for counter-clockwise rotation nor for stationary joints.
RE: High strength fasteners
Thanks for the links. Do you think this is some kind of creep phenonomeon caused by which direction the shaft is rotating?
I found the part about jam nuts interesting too. I would like to see the Junkers test on the left hand threads. The Junkers test of the jam nuts was convincing.